"I firmly support the decisive action taken by President Hollande to strike Isil in Syria, it is my firm belief that we should do so too," Mr Cameron said in a statement.

Mr Hollande said France planned to intensify its air strikes on Islamic State (IS) targets in Syria.

"We will intensify our strikes, choosing targets that will do the most damage possible to this army of terrorists," Mr Hollande said.

The French president kicks off a week of diplomatic efforts to rally support to crush the group: after meeting Mr Cameron on Monday, he will meet US President Barack Obama on Tuesday, German Chancellor Angela Merkel on Wednesday and Russian President Vladimir Putin on Thursday.

Earlier, Mr Hollande and Mr Cameron visited the Bataclan concert hall, where at least 89 people were killed.

The French government says the aircraft carrier, Charles de Gaulle, will be operational in the Mediterranean on Monday and ready to act against IS militants in Syria.

Brussels has been on lockdown all weekend amid a manhunt for Abdeslam, who is suspected of being among the assailants who killed 130 people in Paris on Friday.

Mr Michel told reporters that authorities feared "an attack similar to the one in Paris, with several individuals who could also possibly launch several attacks at the same time in multiple locations".

Meanwhile, the BBC understands that another of the suspected attackers - pictured in a new French police appeal issued on Sunday - arrived in Greece under the name of M al-Mahmod.

The BBC's Ed Thomas has matched the image released by French police with a photo on the arrival papers of a man who reached the Greek island of Leros on 3 October.

French police have asked for more information about the man, who they say was the third suicide bomber to strike the Stade de France on 13 November.

Earlier, Belgian Interior Minister Jan Jambon said the danger to Belgium was not tied to Abdeslam alone.

Image copyrightEPAImage caption
Police have released an image of one of the attackers, asking for more information about him

"The threat is broader than the one suspected terrorist," he told Flemish broadcaster VRT.

It was not clear if Mr Jambon was referring to those involved in the Paris attacks, or others who might be planning attacks in Belgium.

Soldiers joined police officers on patrols in Brussels over the weekend. Many public spaces in the usually bustling capital were deserted, as people heeded official warnings to avoid crowds.

Mohammed Abdeslam, the brother of Brahim Abdeslam who blew himself up in Paris and Salah Abdeslam, spoke to Belgian TV on Sunday to urge his fugitive brother to hand himself in.

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